Spatial and temporal development of deltamethrin resistance in malaria vectors of the Anopheles gambiae complex from North Cameroon

Abstract

The effectiveness of insecticide-based malaria vector control interventions in Africa is threatened by the spread and intensification of pyrethroid resistance in targeted mosquito populations. The present study aimed at investigating the temporal and spatial dynamics of deltamethrin resistance in An . gambiae s . l . populations from North Cameroon. Mosquito larvae were collected from 24 settings of the Garoua, Pitoa and Mayo Oulo Health Districts (HDs) from 2011 to 2015. Two to five days old female An . gambiae s . l . emerging from larval collections were tested for deltamethrin resistance using the World Health Organization’s (WHO) standard protocol. Sub samples of test mosquitoes were identified to species using PCR-RFLP and genotyped for knockdown resistance alleles ( Kdr 1014F and 1014S) using Hot Ligation Oligonucleotide Assay (HOLA). All the tested mosquitoes were identified as belonging to the An . gambiae complex, including 3 sibling species mostly represented by Anopheles arabiensis (67.6%), followed by Anopheles coluzzii (25.4%) and Anopheles gambiae (7%). Deltamethrin resistance frequencies increased significantly between 2011 and 2015, with mosquito mortality rates declining from 70–85% to 49–73% in the three HDs (Jonckheere-Terstra test statistic ( JT) = 5638, P < 0.001), although a temporary increase of mortality rates (91–97%) was seen in the Pitoa and Mayo Oulo HDs in 2012. Overall, confirmed resistance emerged in 10 An . gambiae s . l . populations over the 24 field populations monitored during the study period, from 2011 to 2015. Phenotypic resistance was mostly found in urban settings compared with semi-urban and rural settings ( JT = 5282, P < 0.0001), with a spatial autocorrelation between neighboring localities. The Kdr 1014F allelic frequencies in study HDs increased from 0–30% in 2011 to 18–61% in 2014–2015 ( JT = 620, P <0.001), especially in An . coluzzii samples. The overall frequency of the Kdr 1014S allele was 0.1%. This study revealed a rapid increase and widespread deltamethrin resistance frequency as well as Kdr 1014F allelic frequencies in An . gambiae s . l . populations over time, emphasizing the urgent need for vector surveillance and insecticide resistance management strategies in Cameroon.

Review of malaria situation in Cameroon: technical viewpoint on challenges and prospects for disease elimination

“…arabiensis is mainly a metabolic detoxification mechanism. However, over recent years, an increase in the prevalence of target-site resistance, kdr 1014F and 1014S alleles was also reported for this species [92, 167, 251]. Despite widespread distribution of kdr resistance alleles in An.…”

Mapping trends in insecticide resistance phenotypes in African malaria vectors

“…Several studies have reported spatial variation in resistance within a country, but these studies haven't analysed the spatial trends behind this variation [11,12]. In addition, time series of resistance data have shown changes over time at the location of sentinel sites [13][14][15][16][17][18][19][20]; however, only one study has investigated temporal trends across Africa [7]. This study generated a single trend over time for the whole continent, for each species and insecticide, and did not investigate differences in trends between locations.…”

“…Since 2015, deltamethrin has been the only pyrethroid reported to be used in mass IRS campaigns along with DDT and other non-pyrethroid insecticides [4]. Several studies have demonstrated a local increase in insecticide resistance in field mosquito populations following the implementation of LLINs, IRS, or both [19,20,[24][25][26] although in other locations evidence of higher resistance after the introduction of these interventions was not found [24,27]. Associations between agricultural pesticide use and insecticide resistance have also been found [21,28], and there is evidence that pesticide contamination of water bodies is a source of selection pressure for resistance acting on mosquito larvae [29].…”

Mapping Trends in Insecticide Resistance Phenotypes in African Malaria Vectors

“…Sources of insecticides in the environment include the application of insecticide-based vector control interventions for public health, such as LLINs and IRS, and the application of agricultural insecticides, which include the same insecticide classes as those used in vector control 11 . Several studies have demonstrated a local increase in insecticide resistance in field mosquito populations following the implementation of LLINs, IRS, or both 12, 13, 14, 15, 16 although in other locations evidence of higher resistance after the introduction these interventions was not found 12, 17 . Associations between agricultural pesticide use and insecticide resistance have also been found 11, 18 , and there is evidence that pesticide contamination of water bodies is a source of selection pressure for resistance acting on mosquito larvae 19 .…”